Wave Powered Water-Borne Vessel

ABSTRACT

A water-borne vessel for propulsion by incident waves comprises a hull having elongate bow and stern portions having a length greater than its width at its widest point; and a central portion wider than the bow and stern portions. The central portion has a first flared region at the junction with the bow portion and wider than the width of the adjacent region of the bow portion, and a second flared region at the junction with the stern portion and wider than the adjacent region of the stern portion. The central portion being between and wider than the first and second flared regions. The central portion acts to induce the hull to pitch and roll under the action of an incident wave. The vessel further comprises a foil assembly for generating movement of the vessel through the water under the action of an incident wave.

The present invention relates to a water-borne vessel that derives powerfrom the motion of waves.

The use of wave motion to power water-borne vessels is known in the artand has been the subject of considerable research and development forsome time. An early wave powered boat was developed by Herman Linden ofthe Zoological Station, Naples in 1895. The boat comprised fins attachedto each of the bow and stern of the boat. The fins were moved throughthe water and flexed as a result of the normal pitching and rollingmotion of the hull of the boat, thereby generating forward motion of theboat.

GB 551,168 is concerned with the propulsion of boats, rafts and thelike. There is disclosed a propulsive fin having a flexible blade. Thefin is oscillated in the manner of a paddle, to provide propulsion tothe craft.

GB 1,176,559 discloses a flexible fin propulsion member for propelling avessel and a vessel comprising the same. The propulsion member comprisesa generally planar fin having a relatively rigid leading edge portion,the fin decreasing progressively in rigidity in a direction transverseto the direction of motion of the vessel. The trailing edge portion ofthe fin is sufficiently flexible for the fin to be deformed by thepressure of water on the fin to an inclined or declined attitude.

U.S. Pat. No. 3,872,819 concerns a wave actuated horizontal arraystretcher for use in pulling submerged cables, pipes or otherassemblies. The stretcher is attached to a float at the surface of thewater and comprises a plurality of pivotal or flexible fins. Inoperation, the stretcher is submerged below the water surface and thefins are moved by the wave-induced action of the float at the surface.

U.S. Pat. No. 4,332,571 discloses a wave motor. The motor comprises asupporting structure extending from the keel of the vessel into thewater below the hull. A tilting element is provided on the supportingstructure. The tilting element is biased to a neutral, horizontalposition. In operation, the tilting element is moved from the neutralposition by the action of waves on the hull of the vessel, therebygenerating forward motion. The biasing means for the tilting element maybe a spring or comprise a hydraulic piston.

A similar hydraulic system to that of U.S. Pat. No. 4,332,571 isdisclosed in U.S. Pat. No. 4,371,347. In this later system, thesupporting structure is arranged to move vertically with respect to thehull of the vessel, its movement being restrained by a hydraulicactuating system.

During the 1980's, the Hitachi Zosen Corporation began development of awave-powered vessel. The vessel employed either two horizontal finsmounted side by side under the bow of the vessel or a single foilassembly, again mounted under the vessel bow. Vertical motion of thefins through the water pulls the vessel along.

More recently, U.S. Pat. No. 7,371,136 entitled ‘Wave power’ concerns awave powered water vehicle. The vehicle comprises a surface float and afully submerged swimmer. The float and swimmer are connected by atether, as a result of which the swimmer is caused to move up and downdue to the motion of the float induced by incident waves. The swimmercomprises one or more fins. The fins are shaped to induce forward motionof the swimmer as a result of the up and down motion induced by theaction of the float. U.S. Pat. No. 7,371,136 describes a number ofdifferent configurations for the fins. A first configuration comprises afin mounted to rotate about an axis that is displaced from a body of theswimmer. In a second configuration, the fin is mounted to move about anaxis and is provided with an elastic component, separate from the fin,which deforms under the action of the fin to change the orientation ofthe fin. In a third configuration, the fin is provided with a leadingedge. The leading edge comprises a relatively rigid central portionhaving a fixed relationship with the swimmer body and a flexibleoutboard portion. The fins may be arranged to rotate about alongitudinal axis of the swimmer body and are referred to in U.S. Pat.No. 7,371,136 as pectoral fins. The tether may be rigid or elasticallydeformable. The swimmer body may be rigid. Alternatively, the swimmerbody may comprise a flexible portion. A similar assembly is shown anddescribed in U.S. Pat. No. 7,641,524.

JP 2002220082 disclosed a wave-propelled ship equipped with a hydrofoil.

Still more recently, Isshiki, H. et al., ‘Thrust Generation by Waves’,Proceedings of the Ninth (2010) ISOPE Pacific/Asia Offshore MechanicsSymposium, Busan, Korea, Nov. 14-17, 2010, provide an overview ofaspects of use waves to propel sea-going vessels.

There is a need for an improved wave-powered water-borne vessel. Asnoted above, recent developments have concentrated on a vesselcomprising a separate submerged swimmer connected to the vessel by wayof a tether. This is necessarily a complicated arrangement in terms ofits construction, deployment and operation, with the accompanying riskof entanglement with other objects in the water. It would beadvantageous if a simpler system for providing wave-powered propulsionto a vessel could be provided.

It has now been found that the efficiency of a wave powered vessel canbe significantly improved by appropriate design of the hull of thevessel. Prior art vessels comprised hulls that are designed to riseunder the action of the incident waves, in the same manner as the hullof a conventionally powered vessel. It has now been found that anincrease in the power generated from incident waves may be obtained byproviding the vessel with a hull that maximises the movement of the hullinduced by incident waves, in particular pitching and rolling motions ofthe hull, and which minimises drag resistance to motion through thewaves. Drag resistance is reduced by shaping the hull and/or the bow andstern of the hull to cut through the incident waves, rather than risingunder the action of the waves. This is in contrast to the hulls of theprior art vessels, which were designed to rise and fall with the surfaceof the water as the waves pass the vessel.

The efficiency of the vessel in generating propulsion from incidentwaves is increased by increasing the tendency of the vessel to pitch androll under the action of the waves. In contrast, conventional hulldesign reduces the tendency of the hull to pitch and roll, by the flaredshape of the bow and, more particularly, the stern of the vessel. Inthis way, a conventional hull drives into an incident wave and riseswith the wave, losing energy in the process. It has been found thatthese effects may be achieved by using a novel configuration for thehull of the vessel.

Accordingly, in a first aspect, the present invention provides awater-borne vessel for propulsion by incident waves, the vesselcomprising a hull, the hull of the vessel comprising:

an elongate bow portion having a length greater than its width at itswidest point;

an elongate stern portion having a length greater than its width at itswidest point; and

a central portion between the bow portion and a stern portion, thecentral portion having a width greater than the widths of the bow andstern portions, the central portion comprising a first flared region atthe junction with the bow portion, the first flared portion having awidth greater than the width of the adjacent region of the bow portion,and a second flared region at the junction with the stern portion, thesecond flared region having a width greater than the width of theadjacent region of the stern portion, the central portion having itswidest point between the first and second flared regions and greaterthan the widths of the first and second flared regions;

wherein the bow and stern portions act to cut through an incident wave;and

wherein the central portion acts to induce the hull to pitch and rollunder the action of an incident wave;

the vessel further comprising a foil assembly for generating movement ofthe vessel through the water under the action of an incident wave.

The vessel of the present invention is buoyant and is borne by the waterat the water surface. For generating propulsion from incident waves viathe motion of the vessel relative to the water, the vessel is providedwith one or more foil assemblies, as described in more detailhereinbelow. Movement of the vessel, in particular forward motion, isprovided by propulsive forces induced by the movement of the foilassemblies through the water. By having the hull of the vessel formed toincrease the tendency of the vessel to pitch and roll under the actionof incident waves, propulsion of the vessel is provided moreefficiently. The elongated form of both the bow and stern portions ofhull allow the hull to cut through waves, allowing the foil assembliesto remain in contact with the water and to remain in motion relative tothe water. In particular, the form of the bow and stern portions allowsthe or each foil assembly to be positioned and maintained within theincident waves, such that the pitching and rolling motion of the hullinduced by the incident waves causes the or each foil assembly to movein the opposite direction to the particle flow of the water in thewaves.

The tendency of the hull to cut through incident waves and to be moresusceptible to pitching and rolling induced by the action of waves onthe vessel is provided by the aforementioned elongated bow and sternportions in conjunction with the flared central portion. In thisrespect, the term ‘elongated’ is a reference to the portion having alength that is significantly greater than its width at the widest point.In particular, the term is preferably a reference to a portion having alength that is several times greater than the width of the portion atits widest point.

The hull of the vessel comprises an elongated bow portion and anelongated stern portion. The bow portion and stern portion may be thesame or different in form, such as length and width. In one preferredembodiment, the bow portion and stern portion have the same general formand comprise substantially the same portion of the hull, in particularbeing of substantially the same length.

The elongated bow portion may have any suitable form that acts to cutthrough an incident wave and reduce the tendency for the bow to rise upor fall down under the action of the wave, as it reaches and passes thebow. In one preferred form, the bow portion has generally flat, planarsides, extending from the upper edge to the lower edge of the hull. Thebow portion is preferably tapered, that is the width of the bow portionincreases along the longitudinal axis of the hull in the direction fromthe bow to the stern of the hull. The bow portion is most preferablysymmetrical about the longitudinal line of the hull extending from thebow to the stern. In one preferred embodiment, the bow portion isgenerally triangular in plan view, more preferably having an outline inplan view that is of an isosceles triangle, with the base of thetriangle extending laterally across the hull. The sides of the triangle,when taken in plan view, may be substantially straight or may be curved,for example concave.

The bow portion may taper from the upper edge or deck of the hull to thelower edge or keel of the hull. To aid in the bow cutting throughincident waves and to minimise the tendency of the bow portion to riseand fall under the action of incident waves, the bow portion ispreferably substantially uniform in cross section extending from theupper edge or deck to the lower edge or keel of the hull. If tapered, asmentioned hereinbefore, the bow portion is most preferably wider at itsupper portion than its lower portion. More preferably, if tapered in thevertical direction, the bow portion is generally triangular in verticalend section along its length.

In embodiments in which the bow portion is tapered in the verticaldirection, part or all of the sides of the bow portion preferably extendat an angle of from 5 to 30° to the vertical axis, more preferably from10 to 25°, still more preferably from 15 to 20°. It is preferred thatthe vertical taper of the bow portion increases in the longitudinaldirection from the bow to the stern.

The stern portion has a similar form to the bow portion. Thus, theelongated stern portion may have any suitable form that acts to cutthrough and incident wave and reduce the tendency for the stern to riseup or fall down under the action of the wave, as it reaches and passesthe stern. As with the bow portion, in one preferred form, the sternportion has generally flat, planar sides, extending from the upper edgeto the lower edge of the hull. The stern portion is preferably tapered,that is the width of the stern portion increases along the longitudinalaxis of the hull in the direction from the stern to the bow. The sternportion is most preferably symmetrical about the longitudinal line ofthe hull extending from the stern to the bow. In one preferredembodiment, the stern portion is generally triangular in plan view, morepreferably having an outline in plan view that is of an isoscelestriangle, with the base of the triangle extending laterally across thehull. The sides of the triangle, when taken in plan view, may besubstantially straight or may be curved, for example concave.

The stern portion may taper from the upper edge or deck of the hull tothe lower edge or keel of the hull. As with the bow portion, to aid inthe stern cutting through incident waves and to minimise the tendency ofthe stern portion to rise and fall under the action of incident waves,the stern portion is preferably substantially uniform in cross sectionextending from the upper edge or deck to the lower edge or keel of thehull. If tapered, as mentioned hereinbefore, the stern portion is mostpreferably wider at its upper portion than its lower portion. Morepreferably, if tapered in the vertical direction, the stern portion isgenerally triangular in vertical end section along its length.

In embodiments in which the stern portion is tapered in the verticaldirection, part or all of the sides of the stern portion preferablyextend at an angle of from 5 to 30° to the vertical axis, morepreferably from 10 to 25°, still more preferably from 15 to 20°. It ispreferred that the vertical taper of the stern portion increases in thelongitudinal direction from the stern to the bow.

Each of the bow and stern portions may be considered to have a ratio oftheir length to their width at their widest point. Generally, the widestregions of the bow and stern portions are preferably situated adjacentthe central portion. In this way, in embodiments in which the bow andstern portions are tapered in the longitudinal direction, they bothincrease in width in the direction towards the central portion.

In the case of the bow portion, the ratio X of the length of the bowportion to the width of the bow portion is preferably at least 2.5. Morepreferably, the ratio X is at least 3.0, still more preferably at least4.0. A ratio X of greater than 4.5 is preferred for many embodiments,more preferably at least 5.0. A ratio X of at least 6.0, more preferablyat least 6.5 has been found to be particularly suitable for manyembodiments. One preferred embodiment has a ratio X of about 7.75.

In the case of the stern portion, the ratio Y of the length of the bowportion to the width of the stern portion is preferably at least 2.5.More preferably, the ratio Y is at least 3.0, still more preferably atleast 4.0. A ratio Y of greater than 4.5 is preferred for manyembodiments, more preferably at least 5.0. A ratio Y of at least 6.0,more preferably at least 6.5 has been found to be particularly suitablefor many embodiments. One preferred embodiment has a ratio Y of about7.75.

The bow and stern portions may have the same relative dimensions, thatis the ratios X and Y may be the same. Alternatively, the ratios X and Ymay be different. In one preferred embodiment, the ratios X and Y arethe same.

The bow and stern portions may be of the same length or of differentlengths. In one preferred embodiment, the bow and stern portions are ofthe same length. In an alternative embodiment, the bow portion is longerthan the stern portion, that is the central portion is displaced towardsthe stern of the hull.

In contrast to the bow and stern portions, the central portion of thehull is relatively wide, compared with the bow and stern portions. Thecentral portion has a flared region adjacent each of the bow and sternportions, each flared region having a width that is greater than that ofthe respective bow and stern portion. The action of the central portionand the flared regions is to cause the hull to pitch and roll under theaction of an incident wave contacting this portion of the hull.

The flared regions of the central portion provide a transition from theelongated form of the bow and stern portions to the generally wider,more bulbous form of the central portion. As noted above, the centralportion is generally of a substantially greater width, at its widestpoint, than both the bow and stern portions. The widest point of thecentral portion is preferably positioned centrally in the centralportion on the longitudinal axis of the hull extending from the bow tothe stern. In general, the central portion has an increased widthrelative to the bow portion and the stern portion, with the increasedwidth being uniform along the vertical axis of the central portion. Inthis way, the central portion has a substantially uniform increasedwidth extending from the upper edge or deck of the hull to the loweredge or keel.

As noted, the flared regions provide a transition between the respectivebow and stern portion and the central portion. In one preferredembodiment, one or both flared regions are arranged to provide the hullwith lift, under the action of an incident wave. This lifting action ispreferably provided by having the flared region provided with anon-uniform width profile in vertical section. More particularly, theflared region is preferably provided with an upper portion and a lowerportion, the upper portion having a width greater than the lowerportion. The upper portion is most preferably disposed above the normalwaterline of the hull, whereby incident waves contact the lower surfaceof the upper portion, thereby generating lift on the hull. This action,in turn induces the hull to pitch and roll. This movement of the hullmoves the or each foil assembly through the water, in turn generatingmovement of the vessel through the water, as described in more detailhereinafter.

The ratio of the width of the upper portion to the width of the lowerportion is preferably at least 1.2, more preferably at least 1.5, stillmore preferably at least 1.75, with a ratio of at least 2.0 beingsuitable for many embodiments. To provide a transition between the hullor stern portion and the central portion, the flared portion is providedwith a transitional surface between the upper portion and the lowerportion. This transitional surface is preferably smooth. Preferably,this transitional surface extends at an angle downwards from the upperedge or deck of the hull in the longitudinal direction towards thecentre of the central portion. In other words, the upper portion of theflared region increases in height and the lower portion of the flaredregion decreases in height in the longitudinal direction to the centreof the central portion.

The flared regions may comprise any suitable portion of length of thecentral portion, sufficient to provide a transition between the bow andstern portions and, preferably, to provide the aforementioned liftingaction. Preferably, each flared region comprises at least 10.0% of thelength of the central portion, more preferably at least 15.0%, stillmore preferably at least 17.5%. A flared region forming about 20.0% ofthe length of the central portion is preferred for many embodiments.

The flared regions may be the same in size and form, or may bedifferent. Preferably, the flared regions are the same and the centralportion is symmetrical about its central lateral axis.

The flared regions of the central portion of the hull may be extendedinto the respective bow and/or stern portions. In this way, the bowand/or the stern portion may be provided with flared regions, adjacentthose of the central portion. In this way, the interaction between anincident wave and the flared regions, giving rise to lifting of the hulland inducing the hull to pitch, is increased and/or accelerated as thewave passes the hull.

In the case of a bow portion comprising a flared region, the flaredregion may extend to be at or adjacent the bow of the hull.Alternatively, and more preferably, the flared region is spaced from thebow, to allow the bow to cut into and enter an incident wave. In suchembodiments, the flared region may be spaced from the bow by 40.0% ofthe length of the bow portion, more preferably at least 50.0%, stillmore preferably at least 60.0%.

Similarly, in the case of a stern portion comprising a flared region,the flared region may extend to be at or adjacent the stern of the hull.Alternatively, and more preferably, the flared region is spaced from thestern, as with the bow portion. In such embodiments, the flared regionmay be spaced from the stern by 40.0% of the length of the sternportion, more preferably at least 50.0%, still more preferably at least60.0%.

As noted above, the central portion is a wide portion of the hull,relative to the bow and stern portions. In particular, the centralportion of the hull preferably has a ratio Z of its length to its widththat is no greater than 8.0. More preferably, the ratio Y is less than6.0, preferably less than 5.0, still more preferably less than 4.0.

As noted above, the central portion is substantially wider at its widestpoint than the widest points of the bow and stern portions. Preferably,the ratio of the maximum width of the central portion to the maximumwidth of the bow or stern portions is at least 2.0, more at least 2.5,still more preferably at least 3.0. A higher ratio is generallypreferred, that is preferably at least 3.5, more preferably at least4.0, still more preferably at least 4.5. A ratio of at least 5.0 isparticularly preferred for many embodiments. A ratio of about 5.5 isparticularly suitable.

The central portion is preferably symmetrical about its longitudinalaxis.

It is to be understood that references to the width of portions of thehull of the vessel are references to the width of the respective portionin a direction laterally and perpendicular to the longitudinal axis ofthe hull at the widest point of the portion.

The hull of the vessel may have any suitable dimensions of length, widthand height. It is an advantage of the hull configuration of the presentinvention that the hull may be applied on a wide range of differentscales, according to need.

The bow, central and stern portion of the hull of the vessel may be ofany suitable length, relative to each other. In a preferred embodiment,the bow portion comprises at least 10.0% of the total length of the hullof the vessel, more preferably 15.0%, still more preferably 20.0% of thetotal length. In one particularly preferred embodiment, the bow portioncomprises about 25.0% of the total length of the hull of the vessel.

Similarly, the stern portion comprises at least 10.0% of the totallength of the hull of the vessel, more preferably 15.0%, still morepreferably 20.0% of the total length. In one particularly preferredembodiment, the bow portion comprises about 25.0% of the total length ofthe hull of the vessel.

The length of the bow and stern portions may be the same or different.Preferably, the bow portion and the stern portion have the same length.

The central portion of the hull preferably comprises less than 80.0% ofthe total length of the hull of the vessel, more preferably 70.0%, stillmore preferably 60.0% of the total length. In one particularly preferredembodiment, the central portion of the hull comprises about 50.0% of thetotal length of the hull of the vessel.

As noted, the bow portion and the stern portion may be the same in sizeand form, or may be different in either form and/or size, for examplelength and/or width. In one preferred arrangement, the bow and sternportions have the same form and are generally of the same size.

The transition between each of the bow and stern portions of the hulland the central portion of the hull is preferably smooth.

To further increase the tendency of the vessel to pitch and roll, thehull of the vessel is preferably without other features commonlyprovided in the design of conventional water-borne vessels to providethe vessel with increased stability. For example, the hull of the vesselis preferably provided with a rounded bilge. Further, it is preferredthat the hull is not provided with a substantial keel, as a keel acts todampen the rolling motion of the hull. Preferably, the hull is notprovided with a keel extending from the bottom of the hull. Stillfurther, the hull is preferably not provided with rubbing strakes.

The vessel of the present invention may comprise a single hull, that isbe of a mono-hull configuration. Alternatively, the vessel may comprisetwo or more hulls of the aforedescribed configuration, for example acatamaran or a trimaran. Preferably, the vessel is a mono-hullconfiguration.

To propel the vessel across the water, the vessel is provided with oneor more foil assemblies. The foil assemblies are arranged such thatvertical motion of the foil assemblies with respect to the watergenerates forward thrust on the foil assemblies and, hence, movementthrough the water of the vessel to which they are attached.

The foil assemblies each comprise one or more foils, movement of whichthrough the water induces thrust to propel the vessel. The foilassemblies may be located at any suitable position on the hull of thevessel. For example, the or each foil assembly may be mounted on a boomor arm assembly extending from the hull, for extending longitudinallyfrom the bow or the stern of the hull and/or laterally to one side ofthe hull. More preferably, the or each foil assembly extends directlyfrom the hull. In this way, the or each foil assembly is less vulnerableto damage.

Suitable foil assemblies are known in the art. In particular, preferredfoil assemblies are those comprising one or more foils that are deformedunder the action of movement of the foil relative to the water, suchthat the foil assumes an hydrofoil form, thereby generating thrust onthe hull of the vessel to move the vessel through the water.

An improved foil assembly providing increased propulsion to a vessel andhaving improved robustness has now been found.

Accordingly, in a further aspect, the present invention provides a foilassembly for a wave-powered, water-borne craft, the foil assemblycomprising:

a substantially rigid leading edge assembly having a first end and asecond end;

a flexible foil extending from the leading edge assembly, the flexiblefoil having an inner edge and a trailing edge; and

a tensioning assembly for tensioning the flexible foil, the tensioningassembly applying a tension to the flexible foil in the direction awayfrom the leading edge assembly and towards the trailing edge of theflexible foil, the tension be provided to the flexible foil at an anglebetween the inner edge and the trailing edge of the flexible foil.

The foil assembly comprises a leading edge assembly, from which aflexible foil extends. The leading edge assembly is substantially rigidin comparison with the flexible foil, such that the foil may flex inrelation to the leading edge assembly with substantially no flexing ofthe leading edge assembly. In use, the foil assembly is mounted to thehull of the vessel such that the leading edge assembly of the foilassembly is presented to the water, that is the leading edge isforwardmost, and the flexible foil extends rearwards from the leadingedge assembly. The flexible foil has an inner edge and a trailing edge.The foil assembly is arranged such that the flexible foil is tensioned,with the tension being applied to the flexible foil at an angle betweenthe inner edge and the trailing edge.

Typically, the foil assembly is mounted to the hull, either directly tothe hull or relative to the hull by means of a mounting assembly, suchthat movement of the foil assembly through the water induces movement ofthe hull. Accordingly, the foil assembly is generally mounted to thehull to generate forward motion to the hull. As a result, the foilassembly is mounted with the leading edge assembly forwardmost andextending generally laterally of the longitudinal axis of the hull.

The leading edge assembly may have any suitable form. The leading edgeassembly supports the foil and assists in providing and maintaining thenecessary tension to the foil. The leading edge assembly may solelyprovide a support function, that is to support the flexible foil. Morepreferably, the leading edge assembly is shaped to provide thrust underthe action of moving through the water. In one preferred embodiment, theleading edge assembly is in the form of a hydrofoil. The hydrofoil ispreferably a symmetrical hydrofoil, that is without camber and hassymmetrical top and bottom surfaces. Suitable hydrofoil forms are knownin the art. One preferred general form for the foil is a NACA form,known in the art of airfoil design, in particular a foil in the NACAfour digit series. As noted above, preferred NACA foils are thosewithout camber, that is the NACA 00 series of foils. Preferably, thehydrofoil has a thickness-to-chord ratio of from 10 to 20%, morepreferably from 12 to 15. A particularly preferred general form for theleading edge assembly is a NACA 0012 to 0015 hydrofoil.

The leading edge assembly may be of any suitable size to support therequired area of foil. Preferably, the leading edge assembly comprisesfrom 10 to 20% of the width of the foil assembly, that is the distancefrom the leading edge to the trailing edge, more preferably about 15%.

The foil assembly is mounted to the hull of a vessel at a first end ofthe leading edge assembly, with the second end of the leading edgeassembly being distal from the hull. The first end of the leading edgeassembly is at or generally towards the longitudinal axis of the hull ofthe vessel, while the second end of the leading edge assembly isgenerally away from the longitudinal axis of the hull. As noted above,the foil assembly may be mounted directly to the hull of the vessel.Alternatively, the foil assembly may be provided with a support assemblyextending from the vessel and to which the foil assembly is mounted.References herein to the foil assembly or parts thereof being mounted tothe hull are to be understood accordingly as including mounting via sucha support assembly.

The foil assembly may be rigidly mounted with respect to the hull, thatis the leading edge assembly is at a fixed position and orientation withrespect to the hull. Alternatively, the foil assembly may be mountedsuch that the leading edge assembly may be rotatable with respect to thehull, that is the leading edge assembly is able to rotate about itsmounting with respect to the vessel hull. Preferably, the leading edgeassembly is mounted so as to be rotatable about a longitudinal axis ofthe leading edge assembly with respect to the hull. In one arrangement,the leading edge assembly is rotatable about an axle extending from themount of the foil assembly and extending within the first end portion ofthe leading edge assembly, with the leading edge assembly able to rotateabout the axle. Means may be provided to limit the rotation of theleading edge assembly with respect to the hull, in particular to limitthe leading edge assembly to rotation through a particular arc. In oneembodiment, rotation of the leading edge assembly with respect to thehull is limited by the tension applied to the flexible foil, with theleading edge assembly otherwise free to rotate without limitation.

The leading edge assembly may be uniform in cross-section along itslength. More preferably, the leading edge assembly is tapered, beingwider in at least one dimension at the first end adjacent or towards thelongitudinal axis of the vessel hull than at the second end distaltherefrom. Preferably, the width of the leading edge assembly in thedirection from the leading edge to the trailing edge at the first end isgreater than the width at the second, distal end. In one preferredembodiment, the ratio of the width of the leading edge assembly at thefirst end to the second end is from 2.0, more preferably at least 2.5,still more preferably at least 3.0.

The second end of the leading edge assembly is preferably rounded. Aparticularly preferred arrangement has the leading edge assemblytapering from the first end to the second end, with the second end beingrounded.

The leading edge assembly may be straight, that is extend with astraight longitudinal axis away from the longitudinal axis of the hullof the vessel. The leading edge assembly may extend substantiallyperpendicular to the longitudinal axis of the hull or be raked at anangle thereto, preferably extending outwards and rearwards of the vessellongitudinal axis. More preferably, the leading edge assembly extendsoutwards from the longitudinal axis of the hull in an arc, in particularin an arc extending rearwards away from the leading edge. The arc may beselected according to such factors as to prevent entanglement of thefoil assembly with lines or objects in the water. The arc of the leadingedge assembly may be variable, for example by having the leading edgeassembly flexed under an applied tensioning force.

The leading edge assembly may be formed from any suitable materials,sufficient to withstand the forces exerted thereon by the incident wavesand the motion of the vessel. Suitable materials include wood, forexample laminated wood, metals, including alloys, especially lightweightmetals and alloys, for example aluminium and alloys thereof, andplastics, in particular fibre reinforced plastics, such as plasticsreinforced with glass or carbon fibres and the like.

The foil assembly further comprises a flexible foil extending from theleading edge assembly. The foil is a flexible membrane and has an inneredge adjacent or towards the longitudinal axis of the hull and atrailing edge.

The inner edge extends from the leading edge assembly to the trailingedge of the flexible foil and is the edge at or towards the longitudinalaxis of the hull of the vessel. The inner edge of the flexible foil ispreferably straight or substantially straight. It is preferred that theinner edge of the flexible foil is arranged to be substantially parallelto the longitudinal axis of the hull of the vessel. However, the inneredge may extend at an angle to the longitudinal axis. If the inner edgeextends at an angle to the longitudinal axis of the hull, it ispreferred that the angle is kept to a minimum, preferably less than 20°,still more preferably less than 15°, more preferably still less than 10°to the longitudinal axis of the hull.

The trailing edge is the rearmost edge of the flexible foil andtypically extends laterally outwards away from the longitudinal axis ofthe hull. In one embodiment, the trailing edge extends generallyperpendicular to the longitudinal axis of the hull. The trailing edge ofthe flexible foil may be straight or substantially straight. In oneembodiment, the trailing is curved and extends in an arc outwards fromthe longitudinal axis of the hull. Preferably, a curved trailing edgeextends in an arc outwards and forwards from the longitudinal axis.

The foil may have any suitable shape. A particularly preferred shape isgenerally triangular, with the inner edge and trailing edge of the foiland the leading edge assembly forming the sides of the triangle. In thisarrangement, the trailing edge of the flexible foil extends from theinner edge to the leading edge assembly, preferably to the second end ofthe leading edge assembly.

The foil is tensioned under the action of the tensioning assembly. Asnoted above, the tensioning assembly applies tension, that is a force,to the foil at an angle between the inner edge and the trailing edge ofthe foil. The applied tension is a force acting away from the leadingedge assembly and towards the trailing edge of the flexible foil. Thetension applied to the flexible foil may be at any angle between theinner edge and the trailing edge of the flexible foil. Preferably, thetensioning force is applied in a direction that bisects the anglebetween the inner edge and the trailing edge of the flexible foil.

The force applied by the tensioning assembly to tension the flexiblefoil is at an angle to the longitudinal axis of the hull of the vessel.In particular, the force is applied to the flexible foil at an acuteangle to the forward direction of the longitudinal axis. The force maybe applied at any suitable angle that evenly tensions the flexible foil.The force applied and the angle are such that the flexible foil presentsthe optimum angle of attack to the moving water when moving both upwardsand downwards through the water, thereby optimising the thrust producedby the foil assembly. The tensioning force may be applied to theflexible foil at an angle of from 5 to 80° to the longitudinal axis ofthe hull, more preferably from 10 to 70°, still more preferably from 10to 60°. An angle in the range of from 10 to 40° to the longitudinal axisis particularly preferred for many embodiments. The angle of thetensioning force will vary according to the particular shape of theflexible foil, in particular if the tensioning force is to be applied atan angle to bisect the angle between the inner edge and the trailingedge of the flexible foil, as in the preferred arrangement.

The angle of incidence of the foil assembly, in particular the leadingedge assembly of the foil assembly is selected to produce forward thrustof the foil assembly to propel the vessel. The angle of incidence may beadjusted, for example, by adjusting the tension applied to the flexiblefoil by the tensioning assembly.

Suitable materials for forming the foil are known in the art and includeany flexible, pliable or elastic materials. Examples of suitablematerials include rubber, for example sheets of natural or syntheticrubber, polymer sheets, for example sheets of polyurethane,polyvinylchloride and polyolefins, and thermoplastic elastomers. Thefoil may be formed by weaving yarns of one or more suitable materials.Alternatively, the foil may be formed by casting, for example. Othertechniques for forming the foil are known in the art. In one embodiment,the material of the flexible foil is elastic.

The material of the foil and its properties should be selected to ensurethat the foil is able to form a hydrofoil shape upon movement throughthe water, both upwards and downwards. Further, the material should beresistant to extended immersion in water, in particular sea water, andresistant to prolonged exposure to light, in particular ultraviolet (UV)light.

The tensioning assembly may comprise any suitable means for applyingtension to the flexible foil in the manner hereinbefore described.Suitable means for applying the required tension to the foil include atensioning member attached at one end to the flexible foil, inparticular to the region of the flexible foil adjacent the intersectionof the inner edge and the trailing edge. The other end of the tensioningmember is secured to the hull or the support assembly holding the foilassembly. The tensioning member is placed under tension, which in turntensions the material of the foil. In one embodiment, the tensioningmember is a line.

The tensioning assembly may comprise an elastic component, such that thetension applied to the flexible foil is elastic. In one embodiment, thetensioning assembly comprises a tensioning member, arranged as describedabove, the tensioning member being elastic or having an elasticcomponent therein. For example, the tensioning member may be an elasticline. Alternatively, the tensioning member may comprise or be connectedto a resilient member, such as a spring.

The tensioning assembly may apply a fixed tension to the flexible foil.Alternatively, and more preferably, the tensioning assembly isadjustable, such that the tension applied to the foil may be varied. Inthis way, the form of the foil assembly in the water may be adjusted tobalance the forces created by the movement of the hull of the vesselwith respect to the water and to optimise the drive generated by thefoil assembly. This will vary according to such factors as the weight ofthe vessel, or the amount of any ballast or payload being carried by thevessel.

As noted above, the leading edge assembly is rigid, that is rigid inrelation to the foil, which is flexible and able to move under action ofmovement upwards and downwards through the water, so as to adopt ahydrofoil shape, thereby inducing thrust on the hull of the vessel. Theleading edge assembly may have some inherent flexibility, in particularresiliency, allowing the leading edge assembly to flex under the actionof the tensioning force applied to the foil by the tensioning assembly.This can assist in maintaining a uniform tension on the flexible foil.

The foil assembly may have any suitable ratio of the length of the foilassembly to the width of the foil assembly at its widest point. In thisrespect, the length of the foil assembly is the distance from the firstend to the second end of the leading edge assembly and the width is thedistance from the leading edge to the trailing edge of the assembly. Theaspect ratio is preferably in the range of from 2.0 to 10.0, morepreferably from 2.5 to 8.0, still more preferably from 3.0 to 7.5. Morepreferably still, the aspect ratio of the foil assembly is from 3.5 to7.0, in particular from 4.0 to 6.0, especially from 4.5 to 5.5. Anaspect ratio of about 5.0 has been found to be particularly advantageousin many embodiments.

To allow for adjustment of the area of the foil assembly, as discussedbelow, means may be provided to vary the area of the flexible foilbetween the leading edge assembly and the trailing edge of the foil. Forexample, the flexible foil may be arranged to be rolled and unrolledabout, the leading edge assembly or a portion thereof.

As noted above, the vessel is provided with at least one, morepreferably a plurality of foil assemblies. Preferably, some or, morepreferably all, of the foil assemblies are of the aspect of the presentinvention hereinbefore described. The total area of the foil assembliesmay be expressed as a percentage of the total area of the horizontalcross-section of the hull of the vessel at the waterline. The total areaof the foil assemblies is preferably from 10 to 40% of the totalwaterplane area of the vessel, that is the horizontal cross-sectionalarea at the waterline of the vessel. More preferably, the total area ofthe foil assemblies is from 15 to 30% of the total waterline area of thevessel.

The position of the waterline on the hull of the vessel will vary inuse, for example according to the ballasting and payload of the vessel.The weight and position of the ballast of the vessel will vary theperiods of pitching and rolling of the vessel under the action ofincident waves. Accordingly, it is preferred that the total surface areaof the foil assemblies in the water is variable, to accommodate changesin the periods of pitching and rolling of the vessel.

Further, it may be necessary to vary the total surface area of the foilassemblies according to the prevailing weather conditions, in particularthe size and nature of the incident waves. In particular, in order toavoid damage to the vessel in particularly heavy weather conditions, itis preferred that the foil assemblies allow the foils to be reefed, asnoted above, and/or fully retracted and stowed. If retractable, the foilassemblies are preferably retractable and stowed above the water lineand out of the water. The ability to raise the foil assemblies from thewater is also an advantage for vessels that are required to enter aharbour or port and to be docked.

The vessel may be provided with any suitable number and configuration offoil assemblies, as required to provide the required propulsion of thevessel. Preferably, the vessel comprises a plurality of foil assemblies,in particular at least two foil assemblies. The foil assemblies may havethe same surface area or a different surface area. The foil assembliesmay be in any suitable arrangement on the vessel.

Preferably, the foil assemblies are arranged to be symmetrical about thelongitudinal axis of the vessel, that is the foil surface area isarranged in a symmetrical manner about the longitudinal axis. In thisway, the rolling motion of the vessel about its longitudinal axis isbalanced.

The foil assemblies are preferably arranged symmetrically about thelateral longitudinal axis of the vessel, that is the foil surface areaforward of the mid-point of the vessel is the same as the foil surfacearea aft of the vessel mid-point. In this way, pitching motion of thevessel about its mid-point is balanced.

The foil assemblies are preferably arranged to have surface area of thefoil displaced from the longitudinal axis of the vessel. In onearrangement, the foil assemblies are displaced from the longitudinalaxis. In this way, the rolling motion of the vessel is more efficientlyconverted by the foil assemblies into motion of the vessel.

In one embodiment, the vessel comprises first and second foilassemblies, with the first foil assembly mounted at or adjacent the bowof the vessel and the second foil assembly mounted at or adjacent thestern of the vessel.

In an alternative embodiment, the vessel comprises a single foilassembly at or adjacent the bow and two foil assemblies at or adjacentthe stern of the vessel. The foil assemblies are sized to balance bothpitching of the vessel fore and aft and to balance rolling of the vesselfrom side to side.

The foil assemblies are arranged to have the foils submerged below thewater surface. The foil assemblies may be arranged to lie within thefootprint of the vessel hull. Alternatively, part or all of the surfacearea of the foil assembly may extend from or lie outside the area of thehull at the waterline. In particular, the part or all of the foilassembly may extend beyond the bow or stern of the vessel or laterallyfrom the hull.

As indicated above, each foil assembly may be mounted directly to thehull of the vessel. Alternatively, the vessel may be provided with afoil support assembly extending from the hull and supporting one or morefoil assemblies. It is advantageous to have the position of the foilassemblies variable, in particular to be able to vary the position ofthe or each foil assembly along the longitudinal axis of the hull of thevessel, that is forwards or rearwards along the vessel, laterally of thehull of the vessel, and/or adjusting the height of the foil assembliesrelative to the water. In this way, the action of the or each foilassembly may be optimised for such factors as the prevailing conditionsand the condition of the vessel, for example its payload or ballast.Means for effecting such adjustment of the position of the foilassemblies is particularly preferred for manned vessels.

As noted above, the action of the incident waves on the hull of thevessel causes the vessel to pitch and roll. The form of the vessel hullof the present invention is designed to enhance the pitching and rollingmotion induced by the action of incident waves, as described above. Thismovement of the hull, and hence the foil assemblies, relative to thewater causes the foil assemblies to generate motion of the hull throughthe water. The pitching and rolling motion of the hull may be increasedor decreased by varying the weight and position of ballast within thehull. In particular, the pitching of the hull is varied by moving theballast along the length of the vessel. The rolling action of the hullmay be varied by altering the vertical position of the ballast in thehull.

In one preferred embodiment, the vessel comprises a ballast and meansfor varying the position of the ballast within the hull. In this way,the vessel may be adjusted to accommodate different wave conditions. Inaddition, by having the position of the ballast variable in this way,the vessel may be adapted to different payloads, while remainingoptimised as far as possible to generate motion of the vessel throughthe water under the action of the foil assemblies.

The vessel may also comprise means to move the vessel, in particular torock the vessel about the longitudinal axis of the hull and/or to pitchthe vessel forward and aft about the lateral midline of the hull. Thisrocking and/or pitching motion of the vessel causes the foil assembliesto move through the water, in turn generating thrust on the vessel andpropelling it through the water. In this way, the vessel may bepropelled using the foil assemblies when in calm water with insufficientor no waves. Suitable means for rocking and/or pitching the vesselinclude one or more electrical generators or a pendulum assembly.

Further, the vessel may be provided with means to move the or each foilupwards or downwards through the water, again to generate thrust topropel the vessel in the case of calm water with insufficient or nowaves.

In one embodiment, the vessel of the present invention is unmanned andcarries an array of sensors, for example to measure one or moreparameters of the environment of the vessel, together with means fortransmitting and receiving data.

Embodiments of the foil assembly and vessel of the present inventionwill now be described, by way of example only, having reference to theaccompanying drawings, in which:

FIG. 1 is a perspective view of a vessel hull according to oneembodiment of the present invention;

FIG. 2 is a plan view of the hull of FIG. 1 in the direction of arrow IIin FIG. 1;

FIG. 3 is a side view of the hull of FIG. 1 in the direction of arrowIII in FIG. 1;

FIG. 4 is a frontal view of the hull of FIG. 1 from the bow in thedirection of arrow IV in FIG. 1;

FIG. 5 a is plan view of a foil assembly according to one embodiment ofthe present invention;

FIG. 5 b is a side view of the foil assembly of FIG. 5 a;

FIG. 6 is a side view of an alternative foil assembly to that of FIGS. 5a and 5 b; and

FIG. 7 is a plan view of a vessel according to the present inventioncomprising a hull of the embodiment of FIGS. 1 to 4 and a foil assemblyof FIG. 5.

Referring to FIG. 1, there is shown a perspective view of a hull of avessel according to one embodiment of the present invention. The hull,generally indicated as 2, is shown with lines corresponding to thecontours of the hull to indicate the general form of the hull. The hullis shown in plan view in FIG. 2, in side elevational view in FIG. 3 andin a front view from the bow in FIG. 4, again with contour lines presentto indicate the shape of the hull, as appropriate.

The hull 2 is shown in the figures in the orientation in which it sitsin the water and the use of such terms as ‘upper’ and ‘lower’ are to beunderstood accordingly. Similarly, the term ‘rearwards’ is indicating adirection away from the bow and towards the stern of the hull, while theterm ‘forwards’ is an indication in the opposite direction, that istowards the bow and away from the stern.

The hull has a generally smooth outer surface. The major features of theshape of the hull are described below. It is to be understood that thetransition from one feature to another is generally smooth, unlessotherwise indicated.

The hull 2 comprises a central portion 4, a bow 6, a bow portion 8extending between the bow and the central portion, a stern 10, and astern portion 12 extending between the stern and the central portion.The hull 2 is symmetrical about both its longitudinal axis 14 and itscentral lateral axis 16. As a result, the bow portion 8 and the sternportion 12 are the same in form and size. Accordingly, the forward halfof the hull 2, extending from the lateral axis 16 to the bow 6 will bedescribed in detail. It is to be understood that the form of the rearportion extending from the lateral axis 16 to the stern is the same.

The hull has an upper edge or deck 20 and a lower edge or keel 22. Thekeel does not extend from the bottom of the hull, so as to provide asmooth bottom surface with minimal resistance to movement through andwith respect to the water.

The bow 6 is provided with an upper rake 24, extending upwards andrearwards from the bow 6, and a lower rake 26, extending downwards andrearwards from the bow. The upper rake 24 is generally convex in formand transitions in a smooth curve to the deck 20. The lower rake 26 issubstantially linear and meets the keel 22 at an angle. The rakes 24, 26of the bow reduce the tendency for the bow to become entangled withlines, debris or the like below the waterline and to minimise windageand wetted area above the waterline. A straight bow would also functionefficiently to cut through and enter the waves.

The bow portion 8 has generally planar opposing sides 30, 32 extendingfrom the deck 20 to the keel 22. The bow portion 8 is viewed in planview in FIG. 2 and can be seen to be tapered and increase in widthextending rearwards from the bow 6. In plan view, the bow portion issubstantially triangular, with the base of the triangle extendinglaterally across the hull and the sides extending substantially straightin the rearwards direction. A more concave form may be provided to thesides of the triangle if desired.

The contours of the bow portion may also be seen in a vertical view inFIG. 4 and can be seen to taper inwards in the vertical directionextending from the deck 20 to the keel 22.

The form of the bow portion 8 is to allow it to cut into and throughwaves that are incident on the hull 2 and to prevent the bow portionfrom rising upwards or falling downwards under the action of theincident wave.

The central portion 4 has a flared region 40. The flared region 40provides a transition between the bow portion 8 and the central portion4. The flared portion 40 tapers laterally outwards in the rearwardsdirection and has opposing sides 42, 44 of a generally concave form.Referring to FIG. 3, the flared region 40 has an upper flared portion 46and a lower portion 48. The upper flared portion 46 has a greater widththan the lower portion 48 and is arranged to be above the normalwaterline of the hull 2. A transitional surface 50 lies between theupper flared portion 46 and the lower portion 48 and extends rearwardsand downwards to the keel 22 at a point 52.

The central portion 4 to the rear of the flared region and the point 52has a generally rounded, bulbous shape extending to the central lateralaxis 16, where the central portion is at its widest. As shown in FIG. 4,the central portion has opposing outer surfaces 60, 62 which extendsubstantially vertically between the deck 20 and keel 22.

In operation, a wave is incident at the bow 6 of the vessel. The form ofthe bow portion 8 causes the bow portion to cut into and enter the wavewith little or no action of the wave lifting the bow 6. The wavecontacts the flared region 40 of the central portion, in particular thesurfaces 42 and 44. The wave contacts the transitional surface 50 andthe flared upper portion 46 of the flared region 40. This action causesthe hull to be lifted at the flared region 40. In cases where theincident wave is symmetrical on both sides of the hull 2, the lift onthe upper portions 46 of each side of the flared surface issubstantially the same, causing the hull to pitch. In cases where theincident wave is asymmetrical to the hull, the action of the wavecontacting the flared region 40 is a combined pitching and rollingmotion of the hull.

The upper flared portions 46 of the flared regions of the centralportion 4 may extend from the central portion along the upper portion ofthe rearmost part of the bow portion 8. In this way, the interactionbetween the incident wave and the flared regions 40 may occur soon inthe passage of the wave along the hull of the vessel, in turn increasingand/or accelerating the lifting action of the hull to so to increase theinduced pitching motion.

The hull of FIGS. 1 to 4 may be used with a variety of different foilassemblies. The degree of pitching and rolling induced by the shape andform of the hull interacting with the water of an incident wave causesthe foil assemblies to move through vertically through the water, inturn generating thrust and causing the vessel to move through the water.A preferred foil assembly is shown in FIGS. 5 a and 5 b and described indetail below.

Referring to FIGS. 5 a and 5 b, there is shown a foil assembly for usein propelling a water borne vessel under the action of incident waves.The foil assembly, generally indicated as 102, comprises a leading edgeassembly, generally indicated as 104, and a flexible foil, generallyindicated as 106.

The leading edge assembly 104 has a first end 110 and a generallyrounded second end 112. The foil assembly is mounted to a vessel andarranged such that the first end 110 is adjacent or towards thelongitudinal axis of the hull of the vessel and the second end 112 isdistal thereof.

The leading edge assembly 104 comprises a stiff, generally tubularleading edge member 120 formed from glass fibre reinforced plastic. Theleading edge member 120 has the profile of a hydrofoil, in particularthe general form of a NACA 0012 to 0015 foil, with a leading edge 122generally facing the intended direction of travel of the vessel. Theleading edge member 120 is generally arcuate, being curved rearwards,that is away from the leading edge 122, in moving from the first end 110to the second end 112.

The foil assembly 2 is mounted to the vessel, either directly to thehull or to a foil support assembly, by means of a mounting shaft or spar124 extending into the leading edge member 120 from the first end. Theleading edge member 120 may be fixed in relation to the mounting shaftor spar 124 or may be rotatably mounted on the shaft.

The flexible foil 106 comprises a generally triangular sheet ofpolyurethane. The foil 106 has a leading edge portion 130 attached tothe leading edge member 120, for example by a suitable adhesive. Thefoil 106 further has an inner edge 132 extending rearwards from thefirst end 110 of the leading edge assembly 104 and a trailing edge 134.The trailing edge 134 extends from the rearmost end of the inner edge tothe second end 112 of the leading edge assembly 104.

The foil assembly 102 is mounted to the vessel so as to have the inneredge 132 of the foil 106 extending substantially parallel to thelongitudinal axis of the hull of the vessel.

A tensioning assembly, generally indicated as 140, comprises atensioning member in the form of a line 142 attached to an eyelet ring144 in the portion of the foil 106 adjacent the intersection of theinner edge 132 and the trailing edge 134. The line 142 is attachedeither to the hull of the vessel or a suitable support assembly (notshown for clarity) and tensioned, thereby applying a tension to the foil106. As shown in FIG. 5 a, the line 142 extends at an angle to both theinner edge 132 and the trailing edge 134 of the foil 106, therebyapplying a tensioning force to the foil. The tensioning force is appliedto the foil 106 by the line at an angle that substantially bisects theangle between the inner edge 132 and the trailing edge 134.

The line 142 may be elastic or comprise a portion that is elastic.

Turning to FIG. 6, there is shown an alternative configuration for thefoil assembly. Components common to the embodiments of FIGS. 5 a, 5 band FIG. 6 are indicated using the same reference numerals. In theembodiment of FIG. 6, the foil 106 is formed of two plys of material,106 a, 106 b, and extends around the leading edge member 120, as shown.

Finally, referring to FIG. 7, there is shown a plan view of awave-powered, water-borne vessel, generally indicated as 202, comprisinga hull 204 according to the embodiment of the present invention shown inFIGS. 1 to 4 and described above. The vessel 202 further comprises fourfoil assemblies 206 a, 206 b, 206 c, 206 d, according to the embodimentof FIGS. 5 a and 5 b, and described above. The foil assemblies arearranged in pairs, with a two foil assemblies 206 a, 206 b arranged onopposing sides of the bow portion 208 of the hull and two foilassemblies 206 c, 206 d arranged on opposing sides of the stern portion210 of the hull 204. The foil assemblies are shown mounted directly tothe hull 202, by means of spars, as described above in relation to FIG.5 a. The foil assemblies 206 a to 206 d are positioned to be below thenormal waterline of the vessel, so as to remain submerged throughoutsubstantially the entire motion of the vessel. The action of theincident waves causing the hull to pitch and roll, as described above,causes the foil assemblies to rise and fall through the water, in turninducing thrust to drive the hull forwards through the water, that is inthe direction to the left in FIG. 7.

1-48. (canceled)
 49. A water-borne vessel for propulsion by incidentwaves, the vessel comprising a hull, the hull of the vessel comprising:an elongate bow portion having a length greater than its width at itswidest point; an elongate stern portion having a length greater than itswidth at its widest point; and a central portion between the bow portionand a stern portion, the central portion having a width greater than thewidths of the bow and stern portions, the central portion comprising afirst flared region at the junction with the bow portion, the firstflared portion having a width greater than the width of the adjacentregion of the bow portion, and a second flared region at the junctionwith the stern portion, the second flared region having a width greaterthan the width of the adjacent region of the stern portion, the centralportion having its widest point between the first and second flaredregions and greater than the widths of the first and second flaredregions; wherein the bow and stern portions act to cut through anincident wave; and wherein the central portion acts to induce the hullto pitch and roll under the action of an incident wave; the vesselfurther comprising a foil assembly for generating movement of the vesselthrough the water under the action of an incident wave.
 50. The vesselaccording to claim 49, wherein the bow portion and the stern portion areof the same form.
 51. The vessel according to either of claim 49,wherein the bow portion and the stern portion are substantially of thesame length.
 52. The vessel according to claim 49, wherein the bowportion and/or the stern portion has substantially flat, planar sidesextending from the upper edge to the lower edge of the hull.
 53. Thevessel according to claim 49, wherein the ratio X of the length of thebow portion to the width of the bow portion at its widest point and/orthe ratio Y of the length of the stern portion to the width of the sternportion at its widest point is at least 2.5.
 54. The vessel according toclaim 49, wherein one or both of the first and second flared regions hasan upper portion and a lower portion, the width of the upper portionbeing lower than the width of the lower portion, wherein the upperportion is above the normal waterline of the hull when in use.
 55. Thevessel according to claim 54, wherein the ratio of the width of theupper portion to the width of the lower portion is at least 1.2.
 56. Thevessel according to claim 49, wherein the central portion has a ratio Zor its length to its width that is no greater than 8.0.
 57. The vesselaccording to claim 49, wherein the width of the central portion at itswidest point to the maximum width of the bow or stern portion is atleast 2.0.
 58. A foil assembly for a wave-powered, water-borne craft,the foil assembly comprising: a substantially rigid leading edgeassembly having a first end and a second end; a flexible foil extendingfrom the leading edge assembly, the flexible foil having an inner edgeand a trailing edge; and a tensioning assembly for tensioning theflexible foil, the tensioning assembly applying a tension to theflexible foil in the direction away from the leading edge assembly andtowards the trailing edge of the flexible foil, the tension be providedto the flexible foil at an angle between the inner edge and the trailingedge of the flexible foil.
 59. The assembly according to claim 58,wherein the leading edge assembly has the form of a NACA 0012 to 0015foil.
 60. The assembly according to claim 58, wherein the foil assemblyis mounted such that the leading edge assembly is rotatable about itslongitudinal axis with respect to the hull of the vessel.
 61. Theassembly according to claim 60, wherein the foil assembly comprises anaxle extending into a first end of the leading edge assembly, theleading edge assembly being rotatable about the axle.
 62. The assemblyaccording to claim 58, wherein the leading edge assembly extends in anarc outwards and rearwards of the hull of the vessel.
 63. The assemblyaccording to claim 62, wherein the arc is variable.
 64. The assemblyaccording to claim 58, wherein the tensioning force is at an angle offrom 5 to 80° to the forward direction of the longitudinal axis of thehull.
 65. The assembly according to claim 58, wherein the tensioningforce is applied to the flexible foil at an angle to bisect the anglebetween the inner edge and trailing edge.
 66. A water-borne vessel forpropulsion by incident waves, the vessel comprising a hull, the hull ofthe vessel comprising: an elongate bow portion having a length greaterthan its width at its widest point; an elongate stern portion having alength greater than its width at its widest point; and a central portionbetween the bow portion and a stern portion, the central portion havinga width greater than the widths of the bow and stern portions, thecentral portion comprising a first flared region at the junction withthe bow portion, the first flared portion having a width greater thanthe width of the adjacent region of the bow portion, and a second flaredregion at the junction with the stern portion, the second flared regionhaving a width greater than the width of the adjacent region of thestern portion, the central portion having its widest point between thefirst and second flared regions and greater than the widths of the firstand second flared regions; wherein the bow and stern portions act to cutthrough an incident wave; and wherein the central portion acts to inducethe hull to pitch and roll under the action of an incident wave; thevessel further comprising a foil assembly for generating movement of thevessel through the water under the action of an incident wave; the foilassembly comprising: a substantially rigid leading edge assembly havinga first end and a second end; a flexible foil extending from the leadingedge assembly, the flexible foil having an inner edge and a trailingedge; and a tensioning assembly for tensioning the flexible foil, thetensioning assembly applying a tension to the flexible foil in thedirection away from the leading edge assembly and towards the trailingedge of the flexible foil, the tension be provided to the flexible foilat an angle between the inner edge and the trailing edge of the flexiblefoil.
 67. The vessel according to claim 66, wherein the vessel comprisesa plurality of foil assemblies, the foil assemblies being arranged suchthat the surface area of the foil assemblies is symmetrical about themid-point of the vessel hull.
 68. The vessel according to claim 66,wherein the vessel further comprises a drive assembly to move each foilassembly vertically through the water.